Methods for inhibiting hydrate blockage in oil and gas pipelines using amino alcohols and ester compounds

ABSTRACT

A method and an ester composition used therein for inhibiting, retarding, mitigating, reducing, controlling and/or delaying formation of hydrocarbon hydrates or agglomerates of hydrates. The method may be applied to prevent or reduce or mitigate plugging of conduits, pipes, transfer lines, valves, and other places or equipment where hydrocarbon hydrate solids may form under the conditions. At least one ester compound is added into the process stream, where the compound may be mixed with another compound selected from other amino alcohols, esters, quaternary ammonium, phosphonium or sulphonium salts, betaines, amine oxides, amides, simple amine salts, and combinations thereof.

This application claims priority of U.S. provisional patent application 60/513,311 filed on Oct. 21, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the prevention of gas hydrate blockage in oil and natural gas pipelines containing low-boiling hydrocarbons and water. More specifically, the invention relates to a method of controlling gas hydrate blockage through the addition of various chemical compositions.

2. Background of the Related Art

When hydrocarbon gas molecules dissolve in water, the hydrogen-bonded network of water molecules encapsulates the gas molecules to form a -cage-like structure or hydrate. Higher pressures and lower temperatures foster the formation of these structures. These hydrates grow by encapsulating more and more gaseous molecules to form a crystalline mass. The crystalline mass agglomerates to form a larger mass that can result in a plugged transmission line. The hydrocarbon gases that form the majority of the hydrates include methane, ethane, propane, n-butane, iso-butane, n-pentane, iso-pentane, and combinations of these gases.

Thermodynamic hydrate inhibitors, such as methanol or one of the glycols, have traditionally been used to prevent these hydrate formations. These thermodynamic inhibitors are effective at 5-30% (or higher) based on the amount of water. As oil companies are exploring new production in deep waters, the total gas/oil/water productions are also increasing. The use of these thermodynamic inhibitors is not viable in these applications due to logistics.

Kinetic hydrate inhibitors have been identified to prevent these hydrate formations so that the fluids can be pumped out before a catastrophic hydrate formation occurs. The kinetic inhibitors prevent or delay hydrate crystal nucleation and disrupt crystal growth. These kinetic hydrate inhibitors contain moieties similar to gas molecules previously mentioned. It is suspected that these kinetic inhibitors prevent hydrate crystal growth by becoming incorporated into the growing hydrate crystals, thereby disrupting further hydrate crystal growth. The growing hydrate crystals complete a cage by combining with the partial hydrate-like cages around the kinetic hydrate inhibitor moieties containing gas-like groups. These inhibitors are effective with or without the presence of a liquid hydrocarbon phase, but they are typically less effective in preventing the hydrate formation as the production pressure increases. Examples of kinetic hydrate inhibitors include poly(N-methylacrylamide), poly(N,N-dimethylacrylamide), poly(N-ethylacrylamide), poly(N,N-diethylacrylamide), poly(N-methyl-N-vinylacetamide), poly(2-ethyloxazoline), poly(N-vinylpyrrolidone), and poly(N-vinylcaprolactam).

Unlike the kinetic hydrate inhibitors, anti-agglomerate hydrate inhibitors are effective only in the presence of an oil phase. These inhibitors do not inhibit the formation of gas hydrates to the same level as kinetic inhibitors, rather their primary activity is in preventing the agglomeration of hydrate crystals. The oil phase provides a transport medium for the hydrates which are referred to as hydrate slurries so that the overall viscosity of the medium is kept low and can be transported along the pipeline. As such, the hydrate crystals formed in the water-droplets are prevented from agglomerating into a larger crystalline mass.

Examples of several chemicals acting as anti-agglomerate hydrate inhibitors have been reported in U.S. Pat. Nos. 5,460,728; 5,648,575; 5,879,561; and 6,596,911. These patents teach the use of quaternary ammonium salts having at least three alkyl groups with four or five carbon atoms and a long chain hydrocarbon group containing 8-20 atoms. Exemplary compositions include tributylhexadecylphosphonium bromide and tributylhexadecylammonium bromide.

More specifically, Klomp (U.S. Pat. No. 5,460,728) teaches the use of alkylated ammonium, phosphonium or sulphonium compounds having three or four alkyl groups in their molecule, at least three of which are independently chosen from the group of normal or branched alkyls having four to six carbon atoms. Klomp (U.S. Pat. No. 5,648,575) teaches very similar compositions having three or four organic groups in their molecule, at least three of which have at least four carbon atoms, i.e., two normal or branched alkyl groups having at least four carbon atoms and with a further organic moiety containing a chain of at least four carbon atoms. Klomp (U.S. Pat. No. 5,879,561) teaches the use of alkylated ammonium or phosphonium compounds having four alkyl groups, two of which are independently normal or branched alkyls having four or five carbon atoms and two more of which independently represent organic moieties having at least eight carbon atoms.

Klug (U.S. Pat. No. 6,369,004 B1) teaches the kinetic inhibition of gas hydrate formation using polymers based on reacting maleic anhydride with one or more amines. These polymers can also be used together with various other substances, called synergists, including tetrabutylammonium salts, tetrapentylammonium salts, tributylamine oxide, tripentylamine oxide, zwitterionic compounds having at least one butyl or pentyl group on the quaternary ammonium nitrogen atom, such as as Bu₃N⁺—CH₂—COO—. However, kinetic inhibitors are not effective as the pipeline pressure increases.

Rabeony (U.S. Pat. No. 6,015,929) teaches the use of zwitterionic compounds such as R(CH₃)₂N⁺—(CH₂)₄—SO₃— as as anti-agglomerate hydrate inhibitors. The synthesis of this product involves the use of butyl sultone.

However, there remains a need for hydrate inhibitor compounds that effectively prevent agglomeration of hydrates in oil and gas transportation and handling processes. It would be desirable to identify hydrate inhibitor compounds that are effective at higher pressures and/or lower temperatures such as those encounter in deep water production. It would be even more desirable if the same compounds had increased biodegradability.

SUMMARY OF THE INVENTION

The present invention provides yet another method for inhibiting formation of gas hydrate plugs in conduits containing a mixture of hydrocarbons and water. This method comprises adding to the mixture an effective amount of at least one compound having a formula:

wherein: A is N or P; R₁ is a normal or branched alkyl group containing at least 4 carbon atoms; R₂ is hydrogen or an alkyl group containing from 1 to 4 carbon atoms; R₄ is selected from hydrogen, methyl and ethyl; R₅ is either hydrogen or an organic moiety, such as an alkyl chain, containing from 4 to 20 carbon atoms; (X⁻)_(a) is an anion; and a is 0 or 1. When a is 0, then R₃ is selected from —[(CH₂)(CHR₆)_(b)(C═O)]_(c)—O⁻, —[(CH₂CH₂)—(SO₂)]—O⁻, —[(CH₂CH(OH)CH₂)—(SO₂)]—O⁻, and combinations thereof, wherein b is 0 or 1; and c is 0 or 1; and R₆ is selected from hydrogen, methyl, ethyl and combinations thereof. When a is 1, then R₃ is selected from hydrogen, an organic moiety, such as an alkyl or alkenyl group, having from 2 to 20 carbon atoms, and combinations thereof. The X⁻ anion is preferably selected from hydroxide, carboxylate, halide, sulphate, organic sulphonate, and combinations thereof. The preferred halide ions include, without limitation, bromide, chloride, and combinations thereof.

The method may further comprise adding at least one amine salt to the mixture along with the at least one compound. Suitable amine salts include those previously described herein. Furthermore, the at least one compound may be mixed with the solvents previously described herein.

In one embodiment, the at least one compound includes a product of the reaction of N-alkylamine or N,N-dialkylamine with ethylene oxide, propylene oxide or combinations thereof, followed by reacting with at least one alkyl halide having from 1 to 20 carbon atoms.

In a further embodiment, the method comprises introducing ester moieties by trans-esterfication of hydroxy terminals in the alkoxy chains using methyl esters of fatty acids.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of a temperature and pressure profile used in FIGS. 3-17.

FIG. 2 is a graph of sensor activation time (a measure of hydrate formation and blockage) as a function of time for an untreated mixture of hydrocarbon and water.

FIG. 3 is a graph of sensor activation time (a measure of hydrate formation and blockage) as a function of time for a mixture of hydrocarbon and water treated with 3% trimethylhexadecylammonium bromide.

FIG. 4 is a graph of sensor activation time (a measure of hydrate formation and blockage) as a function of time for a mixture of hydrocarbon and water treated with 3% dimethylethylhexadecylammonium bromide

FIG. 5 is a graph of sensor activation time (a measure of hydrate formation and blockage) as a function of time for a mixture of hydrocarbon and water treated with 3% dimethylbutylhexadecylammonium bromide.

FIG. 6 is a graph of sensor activation time (a measure of hydrate formation and blockage) as a function of time for a mixture of hydrocarbon and water treated with 3% dimethylbutyloctadecylammonium bromide.

FIG. 7 is a graph of sensor activation time (a measure of hydrate formation and blockage) as a function of time for a mixture of hydrocarbon and water treated with 3% dipropylbutylhexadecylammonium bromide.

FIG. 8 is a graph of sensor activation time (a measure of hydrate formation and blockage) as a function of time for a mixture of hydrocarbon and water treated with 3% dibutylpropylhexadecylammonium bromide.

FIGS. 9 a and 9 b are graphs of sensor activation time (a measure of hydrate formation and blockage) as a function of time for a mixture of hydrocarbon and water treated with 3% and 1% tributylhexadecylammonium bromide, respectively.

FIG. 10 is a graph of sensor activation time (a measure of hydrate formation and blockage) as a function of time for a mixture of hydrocarbon and water treated with 3% dimethyldihexadecylammonium bromide.

FIG. 11 is a graph of sensor activation time (a measure of hydrate formation and blockage) as a function of time for a mixture of hydrocarbon and water treated with 3% N,N-dibutyl-cocoamidopropyl carbomethoxy betaine.

FIG. 12 is a graph of sensor activation time (a measure of hydrate formation and blockage) as a function of time for a mixture of hydrocarbon and water treated with 3% N,N-dibutylamino-cocoamidopropylamine oxide.

FIG. 13 is a graph of sensor activation time (a measure of hydrate formation and blockage) as a function of time for a mixture of hydrocarbon and water treated with 3% N,N,N-tributyl-cocoamidopropylammonium bromide.

FIG. 14 is a graph of sensor activation time (a measure of hydrate formation and blockage) as a function of time for a mixture of hydrocarbon and water treated with 3% N,N-dibutylhexadecyl-cocoamidopropylammonium bromide.

FIGS. 15 a and 15 b are graphs of sensor activation time (a measure of hydrate formation and blockage) as a function of time for a mixture of hydrocarbon and water treated with 3% and 1% N,N-dibutylhexadecyltriethoxyammonium bromide, respectively.

FIGS. 16 a and 16 b are graphs of sensor activation time (a measure of hydrate formation and blockage) as a function of time for a mixture of hydrocarbon and water treated with 3% and 1% tributylhexadecylphosphonium bromide, respectively.

FIGS. 17 a and 17 b are graphs of sensor activation time (a measure of hydrate formation and blockage) as a function of time for a mixture of hydrocarbon and water treated with 3% and 1%, respectively, of a blend of N,N-dibutyl-cocoamidopropyl carboethoxy betaine and amine salt.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

This invention relates a method and a composition used therein for inhibiting, retarding, mitigating, reducing, controlling and/or delaying formation of hydrocarbon hydrates or agglomerates of hydrates. The method may be applied to prevent or reduce or mitigate plugging of conduits, pipes, transfer lines, valves, and other places or equipment where hydrocarbon hydrate solids may form under the conditions.

The term “inhibiting” is used herein in a broad and general sense to mean any improvement in preventing, controlling, delaying, reducing or mitigating the formation, growth and/or agglomeration of hydrocarbon hydrates, particularly light hydrocarbon gas hydrates in any manner, including, but not limited to kinetically, thermodynamically, by dissolution, by breaking up, other mechanisms, or any combinations thereof.

The term “formation” or “forming” relating to hydrates is used herein in a broad and general manner to include, but are not limited to, any formation of hydrate solids from water and hydrocarbon(s) or hydrocarbon gas(es), growth of hydrocarbon hydrate solids, agglomeration of hydrocarbon hydrates, accumulation of hydrocarbon hydrates on surfaces, any deterioration of hydrate solids plugging or other problems in a system and combinations thereof.

The present method is useful for inhibiting hydrate formation for many hydrocarbons and hydrocarbon mixtures. The method is particularly useful for lighter or low-boiling, C₁-C₅, hydrocarbon gases or gas mixtures at ambient conditions. Non-limiting examples of such “low-boiling” gases include methane, ethane, propane, n-butane, isobutane, isopentane and mixtures thereof. Other examples include various natural gas mixtures that are present in many gas and/or oil formations and natural gas liquids (NGL). The hydrates of all of these low-boiling hydrocarbons are also referred to as gas hydrates. The hydrocarbons may also comprise other compounds including, but not limited to CO₂, hydrogen sulfide, and other compounds commonly found in gas/oil formations or processing plants, either naturally occurring or used in recovering/processing hydrocarbons from the formation or both, and mixtures thereof.

The method of the present invention involves contacting a hydrocarbon and water mixture with a suitable compound or composition. When an effective amount of the compound is used, hydrate blockage is prevented. In the absence of such effective amount, hydrate blockage is not prevented.

The contacting may be achieved by a number ways, including mixing, blending with mechanical mixing equipment or devices, stationary mixing setup or equipment, magnetic mixing or other suitable methods, other equipment and means known to one skilled in the art and combinations thereof to provide adequate contact and/or dispersion of the composition in the mixture. The contacting can be made in-line or offline or both. The various components of the composition may be mixed prior to or during contact, or both. As discussed, if needed or desired, the composition or some of its components may be optionally removed or separated mechanically, chemically, or by other methods known to one skilled in the art, or by a combination of these methods after the hydrate formation conditions are no longer present.

Because the present invention is particularly suitable for lower boiling hydrocarbons or hydrocarbon gases at ambient conditions, the pressure of the condition is usually at or greater than atmospheric pressure. (i.e. about 101 kPa), preferably greater than about 1 MPa, and more preferably greater than about 5 MPa. The pressure in certain formation or processing plants or units could be much higher, say greater than about 20 MPa. There is no specific high-pressure limit. The present method can be used at any pressure that allows formation of hydrocarbon gas hydrates.

The temperature of the condition for contacting is usually below, the same as, or not much higher than the ambient or room temperature. Lower temperatures tend to favor hydrate formation, thus requiring the treatment with the composition of the present invention. At much higher temperatures, however, hydrocarbon hydrates are less likely to form, thus obviating the need of carrying out any treatments.

The ammonium, phosphonium, and sulphonium compounds of the present invention may also be connected through one of the organic side chains, such as represented by —R₄, to become a pendent group of many oxygen-containing polymers. Such polymers include, but not limited to polyacrylate, polymethacrylate, copolymers of acrylate and methacrylate, polyacrylamide, polymethacrylamide, copolymers of acrylamide and methacrylamide, and polymers and copolymers of N-vinylcaprctam.

The ammonium, phosphonium, and sulphonium compounds of the present invention may also be connected through one of the organic side chains, such as represented by —R₄, to become a pendent group of nitrogen containing polymers, where the nitrogen is on the polymer backbone. Such nitrogen containing polymers and copolymers can be obtained by the Michael addition reaction between polyethylenimine and acrylic or methacrylic acids. The copolymers may also include N-vinylcaprolactam, N,N-dimethylacrylamide, N-ethylacrylamide, N-isopropylacrylamide, N-butylacrylamide, or N-tert. butylacrylamide. The suitable onium compounds can be attached through the acid moiety using suitable diamino or aminoalcoholic chemicals followed by the salt forming reactions.

Based on the total weight of the composition, the concentration of the onium compound in a solvent should be in the range from about 5 wt % to about 75 wt %, preferably from about 10 wt % to about 65 wt %.

In addition to the ammonium, phosphonium and sulphonium compounds, the composition may also include liquids. These liquids are generally solvents for the virgin solid form of the compounds. Such solvents include, but are not limited to, water, simple alcohols like methanol, ethanol, iso-propanol, n-butanol, iso-butanol, 2-ethyl hexanol; glycols like ethylene glycol, 1,2-propylene glycols, 1,3-propylene glycol, and hexylene glycol; ether solvents like ethylene glycol mono butylether (butyl cellosolve), ethylene glycol dibutyl ether, and tetrahydrofuran; ketonic solvents like methylethylketone, diisobutylketone, N-methylpyrrolidone, cyclohexanone; armatic hydrocarbon solvents like xylene and toluene; and mixtures thereof. The selection of the suitable solvent or combination of solvents are important to maintain a stable solution of the compounds during storage and to provide stability and reduced viscosity for the inhibitor solutions when they are injected against a pressure of 200 to 25,000 psi. The solvent is present in the inhibitor composition in the range from 0 wt % to about 95 wt %, preferably from 20 wt % to about 95 wt %, more preferably from 50 wt % to about 95 wt % of the total composition.

When the compounds of the present invention are added into the mixture of hydrocarbons and water at any concentration effective to inhibit the formation of hydrates under the given conditions. Preferably, the concentration of the active inhibitor compound is between about 0.01 wt % and about 5 wt % based on the water content in the mixture of hydrocarbons and water. More preferably, the inhibitor compound concentration is between about 0.1 wt % and about 3 wt %.

The present invention may also be used in combination with other means of hydrate inhibition such as the use of thermodynamic or kinetic inhibitors discussed in the background section. These other hydrate inhibitors may be of the same or different type of hydrate inhibitor used in the composition. If mixtures of hydrate inhibitors are used, the mixture may be added to the hydrocarbon and water containing process stream through a single port or multiple ports. Alternatively, individual hydrate inhibitors may be added at separate ports to the process stream.

The present invention may also be used in combination with other oil field flow assurance compounds such as, but not limited to, corrosion inhibitors, scale inhibitors, paraffin inhibitors, and asphaltene inhibitors. The hydrate inhibitors may also be used in combination with emulsion breakers or water clarifiers.

Simple Quaternary Ammonium and Phosphonium Compounds

Certain simple quaternary ammonium and phosphonium compounds are suitable for inhibiting formation of gas hydrate plugs in conduits containing a mixture of hydrocarbons and water, by adding to the mixture an effective amount of at least one hydrate inhibitor compound. One preferred family of hydrate inhibitor compounds has the formula:

R₁ is selected from hydrogen and normal or branched alkyls having from 1 to 3 carbon atoms.

R₂ is selected from normal or branched alkyls having from 1 to 4 carbon atoms, preferably exactly 4 carbon atoms. It should be recognized that R₁ and R₂ may be the same or different, such as where R₁ and R₂ each have exactly one carbon atom.

R₃ is an organic moiety having 4 or 5 carbon atoms.

R₄ is an organic moiety having from 2 to 20 carbon atoms. In certain embodiments, R₄ may be selected from alkyl, alkenyl, aryl, arylalkyl, arylalkenyl, alkylaryl, alkenylaryl, glycol and combinations thereof. Alternatively, R₄ may include one or more heteroatoms selected from oxygen, nitrogen, sulfur and combinations thereof. Still further, R₄ may be chemically bound to a polymer. In one embodiment, R₄ is —[(CH₂—CHR₅—O)]_(n)—H, R₅ is selected from a hydrogen, a methyl group, and an ethyl group, and n ranges from 1 to 3.

A is a nitrogen atom (N) or a phosphorus atom (P).

X⁻ is an anion. For example, X⁻ may be selected from hydroxide, carboxylate, halide, sulfate, organic sulphonate, and combinations thereof. Suitably, the X⁻ anion may be a halide ion selected from bromide, chloride, and combinations thereof.

In one preferred embodiment, the at least one compound is the product of a reaction between an organic halide having one of R₁, R₂, R₃, and R₄ and an amine or phosphene having the other three of R₁, R₂, R₃, and R₄. For example, the at least one compound may be the product of a reaction between butyl bromide and an N,N-dimethyl-alkylamine having between 10 and 20 carbon atoms. Suitably, the N,N-dimethyl-alkylamine may be N,N-dimethyl-hexadecylamine.

The method may be performed at any pressure, such as between 100 and 10,000 psi or even greater than 10,000 psi.

Independently, the method may include adding at least one amine salt to the mixture along with the at least one compound. For example, the amine salt may include a cation moiety that is an amine selected from ammonia, dimethylamine, diethylamine, di-n-propylamine, trimethylamine, triethylamine, tri-n-propylamine, tri-iso-propylamine, ethanolamine, diethylethanolamine, triethanolamine, methyl ethanolamine, ethyl ethanolamine, propyl ethanolamine, methyl diethanolamine, ethyl diethanolamine, dimethyl ethanolamine, diethanolamine, dibutylethanolamine, dipropylethanolamine, dibutylpropanolamine, dipropylpropanolamine, morpholine, N-methylmorpholine, N-ethylmorpholine, N-propylmorpholine, dibutylethanolamine, N,N-dibutyl-cocoamidopropylamine, and combinations thereof. Alternatively, the amine salt may include an anionic moiety that is an acid selected from carboxylic acids and inorganic acids. Suitable carboxylic acids include, with limitation, formic acid, acetic acid, propionic acid, butyric acid, glycolic acid, malonic acid, succinic acid, acrylic acid, methacrylic acid, trifluoroacetic acid, methane sulfonic acid and mixtures thereof. Suitable inorganic acids include, without limitation, nitric acid, hydrogen chloride, hydrogen bromide, and mixtures thereof.

Accordingly, the at least one compound may, for example, include at least one of the following: dimethylbutylhexadecylammonium salt; dimethylbutyloctadecylammonium bromide, dimethylbutyldodecylammonium salt; at least one ammonium salt having an ammonium compound selected from trimethylhexadecylammonium, dimethylethylhexadecylammonium, dimethylbutyloctadecylammonium, dimethylbutylhexadecylammonium, dimethylbutyldodecylammonium, dimethylbutyltetradecylammonium, propyldibutylhexadecylammonium, dipropylbutylhexadecylammonium, and mixtures thereof; or at least one phosphonium salt having a phosphonium compound selected from trimethylhexadecylphosphonium, dimethylethylhexadecylphosphonium, dimethylbutyloctadecylphosphonium dimethylbutylhexadecylphosphonium, dimethylbutyldodecylphosphonium, dimethylbutyltetradecylphosphonium, propyldibutylhexadecylphosphonium, dipropylbutylhexadecylphosphonium, and mixtures thereof.

The hydrate inhibitor compound is preferably mixed with a solvent, for example water, simple alcohols, glycols, ethers, ketonic liquids, aromatic hydrocarbons, and combinations thereof. More specifically, preferred solvents include water, methanol, ethanol, iso-propanol, n-butanol, iso-butanol, 2-ethyl hexanol, ethylene glycol, 1,2-prpylene glycols, 1,3-propylene glycol, hexylene glycol, ethylene glycol mono butylether (butyl cellosolve), ethylene glycol dibutyl ether, tetrahydrofuran, methylethylketone, methylisobutylketone, diisobutylketone, N-methylpyrrolidone, cyclohexanone, xylene, toluene, and combinations thereof.

Betaines and Amine Oxides

Other quaternary ammonium and phosphonium compounds, known as betaines and amine oxides, have also been found to be suitable for inhibiting formation of gas hydrate plugs in conduits containing a mixture of hydrocarbons and water, by adding to the mixture an effective amount of at least one hydrate inhibitor compound having the formula: (R₁)(R₂)(R₃)A⁺-[R₄(C═O)]_(m)—O⁻

In accordance with the invention, R₁, R₂, R₃ and R₄ are organic moieties, wherein R₁ is an alkyl having 4 or 5 carbon atoms, R₂ is hydrogen or an alkyl having from 1 to 4 carbon atoms, and R₃ has 2 to 20 carbon atoms. Optionally, R₃ has an amide functionality. In one embodiment, R₃ is —[(CH₂—CHR₅—O)]_(n)—H, R₅ is selected from a hydrogen, a methyl group, and an ethyl group, and n ranges from 1 to 3. R₄ is preferably a normal or branched alkyl group, such as where R₄ is —[CH₂—CHR₅)_(n)]—, n is 0 or 1, and R₅ is hydrogen or an alkyl having from 1 to 3 carbon atoms.

A is N or P; and m is an integer 0 or 1.

The method may optionally include adding at least one amine salt to the mixture along with the at least one compound. Suitable amine salts include those previously described herein.

Preferred betaines may be derived from an amine and an acid, wherein the amine is selected from dibutylhexadecylamine, dibutyltetradecylamine, dibutyloctadecylamine, dibutyloleylamine, butyldicocoylamine, and mixtures thereof and the acid is selected from chloroacetic acid, acrylic acid, methacrylic acid, and mixtures thereof. Whether derived in this or a different manner, suitable betaines include, without limitation,

dibutylhexadecylcarboxypropyl, dibutyltetradecylcarboxypropyl, dibutyloctadecylcarboxypropyl, dibutyloleylcarboxypropyl, butyldicocoylcarboxypropyl, dibutylhexadecylcarboxyethyl, dibutyltetradecylcarboxyethyl, dibutyloctadecylcarboxyethyl, dibutyloleylcarboxyethyl, butyldicocoylcarboxyethyl, dibutylhexadecylcarboxymethyl, dibutyltetradecylcarboxymethyl, dibutyloctadecylcarboxymethyl, dibutyloleylcarboxymethyl, butyldicocoylcarboxymethyl and mixtures thereof. Suitable amine oxides include, without limitation, butylmethylhexadecylamine, butylmethyltetradecylamine, butylmethyloctadecylamine, butylethylhexadecylamine, butylethyltetradecylamine, butylethyloctadecylamine, dibutylhexadecylamine, dibutyltetradecylamine, dibutyloctadecylamine, dibutyloleylamine, dibutylcocoylamine, butylpropylhexadecylamine, butylpropyltetradecylamine, butylpropyloctadecylaamine, butylpropyloleoylamine, butyldicocoylamine, and mixtures thereof.

In one embodiment, at least one of R₁, R₂ and R₃ is the amide group —[(R₅—NH—(C═O)—R₆)], R₅ is selected from —(CH₂)_(t)—, —[CH₂—(CHR₇)_(t)]—, —(CH₂—CHR₇O)_(u)—(CH₂)_(t)— and combinations thereof, wherein t is an integer 2 to 4, u is 0 or an integer (1 or greater), R₇ is hydrogen or an alkyl having from 1 to 3 carbon atoms, and R₆ is an organic moiety, for example an alkyl or alkenyl group, having 4 to 20 carbon atoms. Most preferably, R₅ is —(CH₂—CHR₇O)_(u)—(CH₂)_(t)—.

A preferred method comprises adding to the mixture an effective amount of at least one compound having a formula: (R₁)(R₂)(R₃)A⁺-[R₄—(C═O)]_(m)—O⁻ where: A is N or P; R₁ is an alkyl having 4 or 5 carbon atoms; R₂ is hydrogen or an alkyl having from 1 to 4 carbon atoms; R₃ is the amide group —[(R₅—NH—(C═O)—R₆)], wherein R₅ is selected from —(CH₂)_(t)—, —[CH₂—(CHR₇)_(t)]—, —(CH₂—CHR₇O)_(u)—(CH₂)_(t)— and combinations thereof, wherein, t is an integer 2 to 4, u is 0 or an integer (1 or greater), R₇ is hydrogen or an alkyl having from 1 to 3 carbon atoms or a combination thereof, and R₆ is an organic moiety, for example an alkyl or alkenyl group, having 4 to 20 carbon atoms; R₄ is —[CH₂—(CHR₈)_(n)]—, wherein n is 0 or 1 and R₈ is hydrogen or an alkyl having from 1 to 3 carbon atoms; and m is 0 or 1. R₅ is preferably —(CH₂—CHR₇O)_(u)—(CH₂)_(t)—, and R₇ is hydrogen, u is 0 or 1, and t is most preferably 3. In one embodiment, R₁ and R₂ are butyl groups. Amides

Further still, the method may include adding to the mixture an effective amount of at least one amide compound having a formula:

where: R₁, R₂, R₄, and R₅ are organic moieties; R₁ is an alkyl having from 4 to 5 carbon atoms; R₂ is hydrogen or an alkyl having from 1 to 4 carbon atoms; R₄ is selected from —(CH₂)_(t)—, —[CH₂—(CHR₆)_(t)]—, —(CH₂—CHR₆O)_(u)—(CH₂)_(t)— and combinations thereof, wherein, t is an integer 2 to 4, u is 0 or an integer (1 or greater), R₆ is hydrogen or an alkyl having from 1 to 3 carbon atoms; R₅ is an organic moiety, such as an alkyl or alkenyl group, having 4 to 20 carbon atoms; A is N or P; X⁻ is an anion; and a is 0 or 1. When a is 0, then R₃ is selected from —[(CH₂)(CHR₆)_(b)(C═O)]_(c)—O⁻, —[(CH₂CH₂)—(SO₂)]—O⁻, —[(CH₂CH(OH)CH₂)—(SO₂)]—O⁻, —[(CH₂)_(n)—(C═S)]—S⁻ and combinations thereof, wherein b is 0 or 1, c is 0 or 1, n is 2 or 3, and R₆ is selected from hydrogen, methyl, ethyl and combinations thereof. When a is 1, then R₃ is selected from hydrogen, an organic moiety, for example an alkyl group, having from 1 to 20 carbon atoms, and combinations thereof. Preferably, R₃ is the same as the group containing the amide functionality.

The X⁻ anion is preferably selected from hydroxide, carboxylate, halide, sulphate, organic sulphonate, and combinations thereof. Suitable halide ions include, without limitation, bromide, chloride, and combinations thereof.

In one embodiment, R₃ is hydrogen, a is 1, and the anion X⁻ is selected from hydroxide, carboxylate, halide, sulphate, organic sulphonate, and combinations thereof. In another embodiment, a is 0 and —[(CH₂)(CHR₆)_(b)(C═O)]_(c)—O⁻, Preferably, b is 0 or 1; c is 1; and R₆ is selected from hydrogen, methyl, ethyl and combinations thereof. Still further, R₃ may be —O⁻. In a still further embodiment, the at least one amide compound is the reaction product of an N,N-dialkyl-aminoalkylamine with an ester or glyceride. Preferably, the ester or glyceride is derived from a plant source or animal source selected from coconut oil, tallow oil, vegetable oil, and combinations thereof.

The method may further comprise adding at least one amine salt to the mixture along with the at least one compound. Suitable amine salts include those previously described herein. Furthermore, the at least one compound may be mixed with the solvents previously described herein.

In another embodiment, the at least one compound includes a product prepared by the reaction of an amine selected from (3-dialkylamino)propylamine and (3-dialkylamino)ethylamine with vegetable oil or tallow oil followed by reacting with a reactant selected from an organic halide, such as an alkyl halide, having from 4 to 20 carbon atoms, hydrogen peroxide, and an acid, wherein the acid is selected from mineral acids, formic acid, acetic acid, chloroacetic acid, propionic acid, acrylic acid, and methacrylic acid, and wherein the dialkyl of the (3-dialkylamino)propylamine includes two alkyl groups independently selected from methyl, ethyl, propyl, butyl, morpholine, piperidine, and combinations thereof.

Amino alcohols and Ester-1 Compounds

The present invention provides yet another method for inhibiting formation of gas hydrate plugs in conduits containing a mixture of hydrocarbons and water. This method comprises adding to the mixture an effective amount of at least one compound having a formula:

wherein: A is N or P; R₁ is a normal or branched alkyl group containing at least 4 carbon atoms; R₂ is hydrogen or an alkyl group containing from 1 to 4 carbon atoms; R₄ is selected from hydrogen, methyl and ethyl; R₅ is either hydrogen (H) or an organic, moiety, such as an alkyl chain, containing from 4 to 20 carbon atoms; (X⁻)_(a) is an anion; a is 0 or 1; n is from 1 to 3; and m is 0 or 1. When a is 0, then R₃ is selected from —[(CH₂)(CHR₆)_(b)(C═O)]_(c)—O⁻, —[(CH₂CH₂)—(SO₂)]—O⁻, —[(CH₂CH(OH)CH₂)—(SO₂)]—O⁻, and combinations thereof, wherein c is 0 or 1; and b is 0 or 1; and R₆ is selected from hydrogen, methyl, ethyl and combinations thereof. When a is 1, then R₃ is selected from hydrogen, an organic moiety, such as an alkyl or alkenyl group, having from 2 to 20 carbon atoms, and combinations thereof. The X⁻ anion is preferably selected from hydroxide, carboxylate, halide, sulphate, organic sulphonate, and combinations thereof The preferred halide ions include, without limitation, bromide, chloride, and combinations thereof.

The method may further comprise adding at least one amine salt to the mixture along with the at least one compound. Suitable amine salts include those previously described herein. Furthermore, the at least one compound may be mixed with the solvents previously described herein.

In one embodiment, the at least one compound includes a product of the reaction of N-alkylamine or N,N-dialkylamine with ethylene oxide, propylene oxide or combinations thereof, followed by reacting with at least one alkyl halide having from 1 to 20 carbon atoms.

In a further embodiment, the method comprises introducing ester moieties by trans-esterfication of hydroxy terminals in the alkoxy chains using methyl esters of fatty acids.

In yet another embodiment, a is 0 and R₃ is —[(CH₂)(CHR₆)_(b)(C═O)]_(c)—O⁻. Preferably, b is 0 or 1, c is 1, and R₆ is hydrogen or a methyl group. Alternatively, R₃ may be —O⁻.

Ester-2 Compounds

The present invention provides still another method for inhibiting formation of gas hydrate plugs in conduits containing a mixture of hydrocarbons and water. This method comprises adding to the mixture an effective amount of at least one compound having a formula:

wherein: A is N or P; R₁ is an alkyl group containing at least 4 carbon atoms; R₂ is hydrogen or an alkyl group containing from 1 to 4 carbon atoms; R₄ is an organic moiety, such as an alkyl, alkenyl or aryl group, containing from 4 to 20 carbon atoms; (X)⁻ is an anion selected from hydroxide, chloride, bromide, sulfate, sulfonate, or carboxylate; and a is 0 or 1. When a is 0, then R₃ is selected from —[(CH₂)(CHR₆)_(b)(C═O)]_(c)—O⁻, —[(CH₂CH₂)—(SO₂)]—O⁻, —[(CH₂CH(OH)CH₂)—(SO₂)]—O⁻, and combinations thereof, wherein b is 0 or 1, and c is 0 or 1; and R₆ is selected from hydrogen, methyl, ethyl and combinations thereof. When a is 1, then R₃ is selected from hydrogen, an organic moiety, for example an alkyl or alkenyl group, having from 4 to 20 carbon atoms, and combinations thereof.

In one embodiment, the at least one compound includes a product of the Michael addition reaction of alkyl or N,N-dialkyl amine with an acrylate, followed by reacting with at least one organic halide, such as an alkyl halide, having from 1 to 20 carbon atoms.

In yet another embodiment, a is 0 and R₃ is —[(CH₂)(CHR₆)_(b)(C═O)]_(c)—O⁻. Preferably, b is 0 or 1, c is 1, and R₆ is hydrogen, methyl, ethyl or a combination thereof. Alternatively, R₃ may be —O⁻. Optionally, the at least one compound includes a product of the reaction of a tertiary amine containing the ester moiety with chloroacetic acid, acrylic acid or methacrylic acid. In accordance with a similar option, the at least one compound includes a product of the reaction of a tertiary amine containing the ester moiety with hydrogen peroxide.

EXAMPLE 1 Test Procedure for Evaluating Hydrate Inhibitor Compounds

The “Rocking Arm” test apparatus used for these evaluations contains “pressure cells” made of sapphire tubing containing a stainless steel ball. The cells are placed in a rack, and the rack gently rocked forward, then back. The cells are charged with liquids prior to being placed in the rack and then immersed in an insulated tank containing water. Once the cells are immersed in the bath they can then be charged with gas and the experiment begun. Sensors are used to monitor ball movement within the cells, with one sensor placed near each end of the cell. The ball falling time is recorded. This data is referred to as Sensor Activation Time and they are noted as Sensor-1 and Sensor-2.

In a typical experiment, the cells were charged with oil to brine ratios ranging from 10:1 to 1:10. A typical oil to brine ratio is about 2:1. The hydrate inhibitors were mixed with the solutions in the cells. The cells were purged with a synthetic natural gas blend, then charged with gas to the desired pressure and allowed to equilibrate at the pre-determined temperature. The bath was then cooled to a lower pre-determined temperature at specified rates. The following parameters were recorded: (1) bath temperature, (2) individual cell pressure, (3) sensor activation time, and (4) visual observations. Hydrate formation or blockage is indicated by either an increase in sensor activation time (SAT) or visual observation of hydrate particles sticking to the walls. When evaluating the sensor data the results can indicate: (1) a viscosity increase due to the formation of hydrates, which can also be due in part to oil effects; (2) a partial blockage; and (3) a complete blockage.

The inhibitor evaluations were conducted using a synthetic natural gas blend shown in Table 1. The composition of the synthetic salt water (brine) used for the inhibitor evaluations is presented in Table 2. A typical temperature-pressure profile is presented in FIG. 1. A list of inhibitor compounds that were evaluated and the results of the evaluations are summarized in Table 3 and in FIGS. 2-17. Each of these inhibitor compounds was tested as an inhibitor solution at a 3 volume % dosage rate. Each inhibitor solution was made up of 40 wt % inhibitor compound and 60 wt % solvent, wherein the solvent itself was a mixture of half xylene and half n-butanol. TABLE 1 Gas Composition Synthetic Blend Components Mol % Nitrogen 0.4 Methane 87.2 Ethane 7.6 Propane 3.1 i-Butane 0.5 n-Butane 0.8 i-Pentane 0.2 n-Pentane 0.2

TABLE 2 Composition of Synthetic brine Concentrations of Individual Ions Ions (mg/L) Sodium 24000 Potassium 250 Calcium 2800 Magnesium 990 Barium 14 Strontium 95 Chloride 45019 Bromide 2200

TABLE 3 Inhibitor Compounds Evaluated Inhibitor FIGURE # Inhibitor Performance  2 None Complete hydrate blockage at 9° C. (48.2° F.).  3 Trimethylhexadecylammonium Partial hydrate blockage at 6° C. (42.8° F.). bromide Later on, the hydrate broke lose.  4 Dimethylethylhexadecylammonium Partial hydrate blockage at 4.4° C. (40° F.). bromide Later on, the hydrate broke lose.  5 Dimethylbutylhexadecylammonium No hydrate blockage at 4.4° C. (40° F.) in bromide 18 hours.  6 Dimethylbutyloctadecylammonium No hydrate blockage at 4.4° C. (40° F.) in bromide 13 hours.  7 Dipropylbutylhexadecylammonium No hydrate blockage at 4.4° C. (40° F.) in bromide 13 hours.  8 Dibutylpropylhexadecylammonium No hydrate blockage at 4.4° C. (40° F.) in bromide 13 hours.  9 a & b Tributylhexadecylammonium bromide No hydrate blockage at 4.4° C. (40° F.) in 13 hours with 3% inhibitor; complete hydrate blockage with 1% inhibitor. 10 Dimethyldihexadecylammonium Complete hydrate blockage at 11° C. bromide (51.8° F.). 11 N,N-Dibutyl-cocoamidopropyl No hydrate blockage at 4.4° C. (40° F.) in carbomethoxy betaine 13 hours. 12 N,N-Dibutylcocoamidopropylamine No hydrate blockage at 4.4° C. (40° F.) in oxide 13 hours. 13 N,N,N-Tributyl- No hydrate blockage at 4.4° C. (40° F.) in cocoamidopropylammonium bromide 13 hours. 14 N,N-Dibutylhexadecyl- No hydrate blockage at 4.4° C. (40° F.) in cocoamidopropylammonium bromide 13 hours. 15 a & b N,N- No hydrate blockage at 4.4° C. (40° F.) in Dibutyltriethoxyhexadecylammonium 13 hours with 1 and 3% inhibitor. bromide 16 a & b Tributylhexadecylphosphonium No hydrate blockage at 4.4° C. (40° F.) in Bromide 13 hours with 3% inhibitor; initial hydrate blockage with 1% inhibitor. 17 a & b Blend of N,N-Dibutyl- No hydrate blockage at 4.4° C. (40° F.) in cocoamidopropyl carboethoxy betaine 13 hours with 1 and 3% inhibitor. and amine salt

The above examples are intended to illustrate the performance of the new inhibitors. These examples are not intended and should not be interpreted to limit their applicabilities under any other conditions such as pressure, gas composition, amount and type of oil, amount and type of water (salinity). Please also note that the performance ranking of the inhibitors noted here may be changed or reversed under a different set of conditions.

The terms “comprising,” “including,” and “having,” as used in the claims and specification herein, shall be considered as indicating an open group that may include other elements not specified. The term “consisting essentially of,” as used in the claims and specification herein, shall be considered as indicating a partially open group that may include other elements not specified, so long as those other elements do not materially alter the basic and novel characteristics of the claimed invention. The terms “a,” “an,” and the singular forms of words shall be taken to include the plural form of the same words, such that the terms mean that one or more of something is provided. For example, the phrase “a solution comprising a phosphorus-containing compound” should be read to describe a solution having one or more phosphorus-containing compound. The terms “at least one” and “one or more” are used interchangeably. The term “one” or “single” shall be used to indicate that one and only one of something is intended. Similarly, other specific integer values, such as “two,” are used when a specific number of things is intended. The terms “preferably,” “preferred,” “prefer,” “optionally,” “may,” and similar terms are used to indicate that an item, condition or step being referred to is an optional (not required) feature of the invention.

The disclosure of a range of values, such as a disclosure of a compound having an alkyl having from 6 to 20 carbon atoms, shall be construed as further specifically disclosing each and every individual value there between, such as 7, 8, 9, . . . 18, 19. Still further, the disclosure of lists of alternative components, conditions, steps, or aspects of the invention shall be construed as specifically disclosing each and every combination of those alternatives, unless the combination is specifically excluded or mutually exclusive.

It should be understood from the foregoing description that various modifications and changes may be made in the preferred embodiments of the present invention without departing from its true spirit. It is intended that this foregoing description is for purposes of illustration only and should not be construed in a limiting sense. Only the language of the following claims should limit the scope of this invention. 

1. A method for inhibiting formation of gas hydrate plugs in conduits containing a mixture of hydrocarbons and water, the method comprising: adding to the mixture an effective amount of at least one compound having a formula:

wherein: A is N or P; R₁ is a normal or branched alkyl group containing at least 4 carbon atoms; R₂ is hydrogen or an alkyl group containing from 1 to 4 carbon atoms; R₄ is selected from hydrogen, methyl and ethyl; R₅ is either hydrogen or an alkyl chain containing from 4 to 20 carbon atoms; (X⁻)_(a) is an anion; and a is 0 or 1; wherein if a is 0, then R₃ is selected from —[(CH₂)(CHR₆)_(b)(C═O)]_(c)—O⁻, —[(CH₂CH₂)—(SO₂)]—O⁻, —[(CH₂CH(OH)CH₂)—(SO₂)]—O⁻, and combinations thereof, b is 0 or 1, c is 0 or 1, and R₆ is selected from hydrogen, methyl, ethyl and combinations thereof; and wherein if a is 1, then R₃ is selected from hydrogen, an organic moiety having from 2 to 20 carbon atoms, and combinations thereof.
 2. The method of claim 1, wherein X⁻ is an anion selected from hydroxide, carboxylate, halide, sulphate, organic sulphonate, and combinations thereof.
 3. The method of claim 1, wherein the X⁻ anion is a halide ion selected from bromide, chloride, and combinations thereof.
 4. The method of claim 1, further comprising: adding at least one amine salt to the mixture along with the at least one of the claimed compounds.
 5. The method of claim 4, wherein the amine salt includes a cation moiety that is an amine selected from ammonia, dimethylamine, diethylamine, di-n-propylamine, trimethylamine, triethylamine, tri-n-propylamine, tri-iso-propylamine, ethanolamine, diethylethanolamine, triethanolamine, methyl ethanolamine, ethyl ethanolamine, propyl ethanolamine, methyl diethanolamine, ethyl diethanolamine, dimethyl ethanolamine, diethanolamine, dibutylethanolamine, dipropylethanolamine, dibutylpropanolamine, dipropylpropanolamine, morpholine, N-methylmorpholine, N-ethylmorpholine, N-propylmorpholine, dibutylethanolamine, and combinations thereof.
 6. The method of claim 4, wherein the amine salt includes an anionic moiety that is an acid selected from carboxylic acids and inorganic acids.
 7. The method of claim 4, wherein the amine salt includes an anionic moiety that is a carboxylic acid selected from formic acid, acetic acid, propionic acid, butyric acid, glycolic acid, malonic acid, succinic acid, acrylic acid, methacrylic acid, trifluoroacetic acid, methane sulfonic acid and mixtures thereof.
 8. The method of claim 4, wherein the amine salt includes an anionic moiety that is an inorganic acid selected from nitric acid, hydrogen chloride, hydrogen bromide, and mixtures thereof.
 9. The method of claim 1, wherein the at least one compound includes a product of the reaction of N-alkylamine or N,N-dialkylamine with ethylene oxide, propylene oxide or combinations thereof, followed by reacting with at least one alkyl halide having from 1 to 20 carbon atoms.
 10. The method of claim 1, further comprising: introducing ester moieties by trans-esterfication of hydroxy terminals in the alkoxy chains using methyl esters of fatty acids.
 11. The method of claim 1, wherein R₃ is —[(CH₂)(CHR₆)_(b)(C═O)]_(c)—O⁻, and wherein a is 0, b is 0 or 1, c is 1, and R₆ is hydrogen or a methyl group.
 12. The method of claim 1, wherein R₃ is —O⁻.
 13. The method of claim 1, wherein the at least one compound is mixed with a solvents selected from water, simple alcohols, glycols, ethers, ketonic liquids, aromatic hydrocarbons, and combinations thereof.
 14. The method of claim 1, wherein the at least one compound is mixed with a solvents selected from water, methanol, ethanol, iso-propanol, n-butanol, iso-butanol, 2-ethyl hexanol, ethylene glycol, 1,2-prpylene glycols, 1,3-propylene glycol, hexylene glycol, ethylene glycol mono butylether (butyl cellosolve), ethylene glycol dibutyl ether, tetrahydrofuran, methylethylketone, methylisobutylketone, diisobutylketone, N-methylpyrrolidone, cyclohexanone, xylene, toluene, and combinations thereof.
 15. The method of claim 1, wherein n is 1, m is 0, R₄ is hydrogen, and R₅ is hydrogen. 